1. Field of the Invention
The invention relates to a pressure sensor for converting a fluid pressure into an electrical signal, and more particularly, to a pressure sensor of the type including a movable body which is subjected to a fluid pressure, causing a displacement of the movable body which is converted into an electrical signal.
2. Description of the Prior Art
A conventional arrangement is known in which a diaphragm is subject to a fluid pressure and is normally urged by a coiled spring against the fluid pressure, the diaphragm being connected to a slider on a potentiometer. In this arrangement, the potentiometer provides an analog voltage corresponding to the amount of movement of the diaphragm when the latter is subjected to a fluid pressure. In this pressure sensor, it is desirable for a thin film resistor forming the potentiometer to have a low sliding friction and provide a stable output voltage for a given slider position. It is also desirable that the movable body and the slider by mechanically connected together with a minimal degree of rattling and that a stabilized contact be maintained between the slider and the thin film resistor in the presence of oscillations or shocks. However, because the slider is brought into contact with the thin film resistor under pressure, friction or oscillations may cause an unstable output voltage to be produced at any particular measured fluid pressure.
Recently, significant advances in semiconductor pressure sensors have led to a sensor which includes a semiconductor strain gauge constructed so that a change in the gauge resistance which occurs in response to a pressure applied thereto is converted into an analog voltage. In this arrangement, the semiconductor strain gauge is very small in size. However, since a detecting signal which occurs in accordance with the pressure is very small and since temperature drift may be large, this arrangement requires a complex circuit for amplifying the detecting signal and compensating for adverse influences of temperature drift. In addition, the semiconductor is significantly affected by friction or oscillations.